The invention relates to a process for mixing liquid samples to be analysed, in which the liquid sample is placed in a sample container, particularly in a cuvette or cell, and is moved and mixed by an air column that is mechanically oscillated and is in contact with at least part of the liquid sample surface.
In a known process of this type (German Pat. No. 15 98 514), used for performing blood examinations, the liquid to be examined is placed in one leg of a receiving container and the reagent liquid to be added is placed in the other leg of the container, the two legs being interconnected by a capillary channel in the container bottom area. The mouthpiece of a hose is sealingly placed on the opening of one leg and is connected to the cylinder area of a piston pump, so that by a compression movement of the pump piston, the liquid is forced out of the leg carrying the mouthpiece through the capillary channel into the other leg and then, in the case of a corresponding reversal of the piston movement, i.e., during an expansion movement, is sucked back through the capillary channel into the leg carrying the mouthpiece. The frequency of the pump piston movement is preferably 1 Hz.
Quite apart from the fact that in this process a very specially constructed receiving container is required, mixing only takes place very slowly, so that mixing times of approximately 10 seconds are required and this must be followed by settling times of approximately 3 to 4 seconds. Due to this long period of time, which is obviously disadvantageous for the rapid performance of mixing processes, said process is made particularly unsuitable for so-called kinetic measurements, as are used to an increasing extent in clinical and medical laboratories, in which the time sequence of the reaction must be measured within a sample and said reaction process starts immediately following the mixing of the sample constituents.
In another known process (DE-OS No. 26 51 356), sample containers with receiving legs are used in a similar way and are interconnected by narrow channels. Due to the recycling between the receiving legs, a large amount of turbulence occurs in the vicinity of the narrow connecting channels and this leads to intermixing. However, here again, both the mixing time and the settling time are very long.
It is also already known to intermix liquid samples by using ultrasonics, for which purpose an ultrasonic exciter is conventionally brought into direct contact with the liquid sample. This very rapidly leads to a very good intermixing, but such a process frequently cannot be used with liquid samples to be analysed, e.g. from the clinical sector, because these liquid samples contain high molecular weight substances which would be destroyed by ultrasonic action.